The present invention relates to a data recording apparatus, and is particularly suitably applied to a data recording apparatus which is capable of recording information data at different recording speeds.
There is known a data recording system which is capable of high density recording of information data using a helical scanning digital video tape recorder.
The maximum recording speed of such a data recording system depends on the maximum frequency of the high frequency band of the recording system, which includes a record amplification circuit, a rotary transformer and a rotary head.
Here, the data recording system is represented by an equivalent circuit illustrated in FIG. 1.
More specifically, in this data recording system 1, information data DTREC having a predetermined transmission rate (hereinafter referred to as a data rate) is amplified in the record amplification circuit 2, and the resulting record signal SREC is fed to a magnetic head 4 through a rotary transformer 3, so that the information data DTREC is recorded on a magnetic tape 5.
Here, the inductance LS of the rotary transformer 3 represents a loss due to the rotary transformer, and the inductance LH of the magnetic head 4 represents a combined inductance of the rotary transformer 3 and the magnetic head 4. As shown by the characteristic curve in FIG. 2, a maximum frequency fmax of the record signal SREC can be recorded by such a construction.
On the output side of the record amplification circuit 2, there occurs a capacitance CH which is calculated by combining the output capacitance of the record amplification circuit 2 and the distributed capacitance of the circuits, the leads, the rotary transformer 3, etc.
In the data recording system 1, the capacitance CH and the inductances LS and LH of the rotary transformer 3 and the head 4, respectively, produce a resonance circuit, and in the frequency characteristic TO (shown by the solid line in FIG. 2), a rise occurs in the amplitude characteristic in the vicinity of the maximum frequency fmax.
To correct the rise, in the data recording system 1 a damping resistor RH with one end grounded is connected to the output side of the record amplification circuit 2, and thereby the rise of the amplitude characteristic in the vicinity of the maximum frequency fmax is corrected as much as possible to provide a corrected frequency characteristic T1 (indicated by the dot-and-dash line in FIG. 2).
In the data recording system 1, information data DTREC which is typically sent at a data rate of 88 Mbps is recorded as a record signal SREC with a maximum frequency fmax of 44 MHz using magnetized patterns, which represent recording wavelength inverting at minimum intervals of 0.9 .mu.m, formed on the recording tracks of the magnetic tape 5.
Here, when the information data DTREC generating a shorter wave pattern PTNS after a longer wave pattern PTNL are recorded on the magnetic tape as shown in FIG. 3A, the shorter wave pattern PTNS suffers a reduction in amplitude due to an interference wave form HX, as shown FIG. 3B.
To correct for such interference, when the information data DTREC is digitally recorded on the magnetic tape, the front edges of the record signal SREC are emphasized and/or a portion of each longer wave pattern of the record signal SREC is pulse wave modulated within the limits of a half of the minimum wavelength prior to recording.
In a data recording apparatus, a front edge emphasizer (not shown in FIG. 1) is used to emphasize each front edge EG of the record signal SREC, as shown in FIG. 3C, before its is input to the record amplification circuit 2 for recording. In the data recording system 1, the relative speed of the magnetic head 4 to the recording tracks of the magnetic tape 5 can be changed by factors of 1/1 (i.e., multiplied by a factor of 1, indicating the maximum recording rate), 1/2, 1/4, 1/8, 1/16, 1/24, etc., by controlling the rotary speed of the head 4 and the traveling speed of the magnetic tape 5, thus permitting magnetic patterns to be recorded on and reproduced from recording tracks with a minimum recording wavelength of 0.9 .mu.m at different recording and reproducing speeds.
Referring to FIG. 10, the relationship of the information data DTREC recorded on and reproduced from the recording tracks is illustrated. Information data DTREC which has been recorded at a data rate of 88 Mbps (44 MHz), for by controlling the recording speed using a factor of 1 can be read with a data rate of 44 (or 22, 11, 5.50 or 2.25) Mbps by controlling the relative speed of the magnetic tape 5 to the head 4 by a factor of 1/2 (or 1/4, 1/8, 1/16 or 1/24); that is, a data rate with maximum frequency of 22 (or 11, 5.50, 2.25 or 1.25) MHz. This enables the information data DTREC to be reproduced at a speed which is lower by a factor of 1/2 (or 1/4, 1/8, 1/16 or 1/24).
Furthermore information data DTREC which has been recorded at a data rate of 44 Mbps (22 MHz), for example, by controlling the recording speed using a factor of 1/2 can be read with a data rate of 88 Mbps by controlling the relative reproducing speed of the magnetic tape 5 to the head 4 by a factor of 1/1; that is, a data rate with maximum frequency fmax1 of 44 MHz. This enables the information data DTREC to be reproduced at twice its recording speed.
In this data recording system, which is capable of recording and reproducing at different speeds, observed data, such as astronomical observation data, which slowly changes can be recorded at a data rate of 2.25 Mbps, and can be reproduced at a data rate of 88 Mbps. This enables data collected over a long time to be analyzed within a short time.
Furthermore, observation data, measurement data, or data for other events which quickly change may be recorded at a data rate of 88 Mbps and reproduced at a data rate of 2.25 Mbps. The enables the data to be analyzed at a lower speed. Thus, this data recording system may be used as a frequency conversion buffer for information data.
In the data recording system 1 of a conventional construction, the record signal SREC, having a maximum frequency fmax of 44 MHz, is recorded with a frequency characteristic T1 as shown by the dot-and-dash line in FIG. 2. In the case where a record signal SREC with a maximum frequency fmax of 22 MHz, for example, which is a factor of 1/2 times as large as the maximum frequency fmax (44 MHz), is to be recorded, recording is carried out with an ideal frequency characteristic T2 as shown by the two-dots-and-dash line in FIG. 2.
When the frequency characteristic T1, corresponding to recording of the information data DTREC at a data rate of 88 Mbps and the frequency characteristic T2, corresponding to recording of the information data DTREC at a data rate of 44 Mbps , are different, then different magnetized patterns are recorded on the recording tracks even if the magnetized patterns are produced with a minimum recording wavelength of 0.9 .mu.m. The difference between magnetized patterns can be observed in an eye pattern of the reproduction signal.
In FIG. 4A, there is illustrated an eye pattern obtained from a reproduction signal for information data recorded on a magnetic tape with a data rate of 88 Mbps at a relative speed with a factor of 1/1 and reproduced from the magnetic tape with a data rate of 88 Mbps at a relative speed with a factor of 1/1. In FIG. 4B, there is illustrated another eye pattern, obtained from a reproduction signal for information data recorded with a data rate of 44 Mbps at a relative speed with a factor of 1/2 on the magnetic tape and reproduced with a data rate of 88 Mbps at a relative speed with a factor of 1/1 from the magnetic tape. If the magnetized patterns formed on the magnetic tape are the same, then the eye pattern of FIG. 4A should be equal to the eye pattern of FIG. 4B. However the eye pattern of FIG. 4B is worse than the eye pattern of FIG. 4A. This means that error rates of the reproduction signals are not equal when using different data rates.
As a result, it is not possible to maintain compatibility of information data when using different data rates.
In the data recording apparatus 1, generally, a differential coefficient of the recording system and a front edge emphasizing circuit (not shown) in front of the record amplification circuit 2 are set to record the record signal SREC on the tape at data rate of 88 Mbps with a maximum frequency of 44 MHz. However, if the information data DTREC is to be recorded at a data rate of 44 Mbps or 22 Mbps, with a factor of 1/8 or 1/4, the front edge of the information data DTREC is heavily emphasized.
Whenever emphasis of the front edges of the information data DTREC corresponds to its data rate the magnetized patterns for the various data rates are not equal, even if the magnetized patterns are formed on recording tracks with the same minimum recording wavelength. As a result, it is not possible to maintain compatibility of information data when using different data rates.